Special feature

A radiation overdose incident: Initial data

Radiotherapy is a common treatment for cancer patients. Although incidence of error is low, errors can be severe or affect significant numbers of patients. In addition, errors will often not manifest until long periods after treatment. This study describes the development of an incident reporting tool that allows categorical analysis and time trend reporting, covering first 3 years of use.

A radiotherapy-specific incident analysis system was established. Staff members were encouraged to report actual errors and near-miss events detected at prescription, simulation, planning, or treatment phases of radiotherapy delivery. Trend reporting was reviewed monthly.

Reports were analyzed for the first 3 years of operation (May 2004–2007). A total of 688 reports was received during the study period. The actual error rate was 0.2% per treatment episode. During the study period, the actual error rates reduced significantly from 1% per year to 0.3% per year (p < 0.001), as did the total event report rates (p < 0.0001). There were 3.5 times as many near misses reported compared with actual errors.

This system has allowed real-time analysis of events within a radiation oncology department to a reduced error rate through focus on learning and prevention from the near-miss reports. Plans are underway to develop this reporting tool for Australia and New Zealand.

To examine the impact of computerized record and verify (R&V) systems on types of radiotherapeutic error.

Radiation therapy treatment errors reported by therapists at the University of Utah between July 1, 1999 and June 30, 2000 were retrospectively reviewed.

During a 1-year period in which 22,542 external beam radiation therapy treatments were administered, 38 treatment errors (representing 0.17% of external beam treatments administered during this period) were identified and reviewed. Nine cases (0.04% of treatments) representing four types of record and verify (R&V)-related errors were identified, in which the department’s R&V system played a contributory role in the treatment error.

The common denominator among these R&V-related errors was excessive reliance upon the computer system by therapists. R&V systems eliminate some, but not all, pathways of radiotherapeutic error. Although R&V systems have assumed a crucial role in the precise and reproducible delivery of increasingly complex radiation therapy treatments, their inability to eradicate all radiotherapeutic errors coupled with their parallel ability to facilitate certain mistakes mandates vigilance on the part of the radiation therapy team. Radiation therapy treatment procedures must preserve careful oversight of R&V functions to minimize prospects for treatment error.

$\text{Purpose}$: This study was conducted to evaluate the decrease in risk from misadministration of the new Leksell Gamma Knife Model C with Automatic Positioning System compared with previous models.

$\text{Methods and Materials}$: Elekta Instruments, A.B. of Stockholm has introduced a new computer-controlled Leksell Gamma Knife Model C which uses motor-driven trunnions to reposition the patient between isocenters (shots) without human intervention. Previous models required the operators to manually set coordinates from a printed list, permitting opportunities for coordinate transposition, incorrect helmet size, incorrect treatment times, missing shots, or repeated shots.

$\text{Results}$: A risk analysis was conducted between craniotomy involving hospital admission and outpatient Gamma Knife radiosurgery. A report of the Institute of Medicine of the National Academies dated November 29, 1999 estimated that medical errors kill between 44,000 and 98,000 people each year in the United States. Another report from the National Nosocomial Infections Surveillance System estimates that 2.1 million nosocomial infections occur annually in the United States in acute care hospitals alone, with 31 million total admissions.

$\text{Conclusions}$: All medical procedures have attendant risks of morbidity and possibly mortality. Each patient should be counseled as to the risk of adverse effects as well as the likelihood of good results for alternative treatment strategies. This paper seeks to fill a gap in the existing medical literature, which has a paucity of data involving risk estimates for stereotactic radiosurgery.

In this critical review of the current practice of patient dose verification, we first demonstrate that a high accuracy (about 1–2%, 1 SD) can be obtained. Accurate in vivo dosimetry is possible if diodes and thermoluminescence dosimeters (TLDs), the main detector types in use for in vivo dosimetry, are carefully calibrated and the factors influencing their sensitivity are taken into account. Various methods and philosophies for applying patient dose verification are then evaluated: the measurement of each field for each fraction of each patient, a limited number of checks for all patients, or measurements of specific patient groups, for example, during total body irradiation (TBI) or conformal radiotherapy. The experience of a number of centers is then presented,providing information on the various types of errors detected by in vivo dosimetry, including their frequency and magnitude. From the results of recent studies it can be concluded that in centers having modern equipment with verification systems as well as comprehensive quality assurance (QA) programs, a systematic error larger than 5% in dose delivery is still present for 0.5–1% of the patient treatments. In other studies, a frequency of 3–10% of errors was observed for specific patient groups or when no verification system was present at the accelerator. These results were balanced against the additional manpower and other resources required for such a QA program. It could be concluded that patient dose verification should be an essential part of a QA program in a radiotherapy department, and plays a complementary role to treatment-sheet double checking. As the radiotherapy community makes the transition from the conventional two-dimensional (2D) to three-dimensional (3D) conformal and intensity modulated dose delivery, it is recommended that new treatment techniques be checked systematically for a few patients, and to perform in vivo dosimetry a few times for each patient for situations where errors in dose delivery should be minimized.